Good afternoon, dear guests and subscribers of the "Build for Myself" channel!
It turns out that finding out the width of a river is just as easy as determining the height of an object (tree, house, pillar) without climbing on it, as the previous article was written about. "How to determine the height of an object near or at a distance? (5 ways!) ".
The width of the river is calculated almost with the same properties of triangles from the school geometry course. Our distance is found by measuring another distance that is available to us on the shore.
In this article I will describe two methods, one of which requires home-made, and the second method does not require anything at all except school knowledge of geometry :-)))
So the first way:
We need a board and 3 sharp objects (a nail, a needle, a pin, etc.). From these objects on a flat base, we build a right-angled isosceles triangle; this can be done very simply with an improvised method.
After that, we select the two most noticeable points on both sides and combine with them along the line of sight two tops of our device, as shown in the figure below (For ease of perception, I will use Latin letters to designate the segments of the sides: A, B, C, D, etc.).
In other words, we need to determine the length of the segment AB.
We fix the device on the surface of the earth. Further, without shifting it (figure below), we define the beam by another of the legs of the constructed triangle, and, thanks to the innate eye, we select any point D on this straight line. Now, it is enough to remove the device and stick a twig at point C.
We got two perpendicular segments AC and CD. Next, we move with our device in hand along the CD segment towards point D. The task is to find such a point on the straight line CD (let it be point E) so that point A and point C coincided with our tops of the device along the leg and hypotenuse, i.e. lie on straight line segments AE and CD. For simplicity, top view:
Thus, we found the third vertex of the triangle (point E), built on the ground. This ACE triangle is both rectangular and isosceles, angles A and E are equal to 45 degrees. And by measuring the segment CE, you get the distance AC.
Now it is enough to subtract BC from the AS, in the end, getting the width of our AB river.
The second way without using homemade devices:
In this method, we also select the most noticeable two points on two banks A and B, and we install a peg at any point C, chosen on a straight line, so A, B and C lie on the same straight line.
Further, we need to start moving at a right angle from point C, for example, go 10 steps and determine point O. After installing the next peg at point O, we move along the same straight line, but we pass 4, 5 or 6 times less distance than the CO segment. For example, for ease of calculations without a remainder: if CO = 10 steps, then the next path will be reduced by 5 times, therefore the next segment OD will be equal to 2 steps.
Now, it is enough from point D to take a few steps back at a right angle to combine on one a straight line a peg at point O and a point on the opposite bank - point A (in the figure - a red line).
As soon as A and O are combined, then you are standing on point E and I hope you have no doubts that the ODE and OAC triangles are similar with an aspect ratio of 1: 5.
In other words, the segment AC is equal to five segments DE. We make the necessary calculations, find the AC, and then, as in the first method, subtract BC from the AC.
Everything, got the width of the river.
On the ground, everything is done for 7-12 minutes and, subject to truly right angles, the error is from one to three meters, depending on the width of the river and the clarity of vision.
Thank you for your patience and attention. Hope this article was helpful to you!
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